Chem 145
Ethers and Epoxides
Chapter 8
1434-1435
2013-2014
2nd semester
Chapter’s out line
Ethers
 Definition; General formula; Classification and Types
Nomenclature
- Common Names.
- IUPAC Naming.
Physical Properties
General methods of preparation of ethers
A- Dehydration of Alcohols.
B- Williamson Synthesis.
Reactions of ethers
Cyclic Ethers; “Epoxides”
 Definition
General methods of preparation of Epoxides
Reaction of Epoxides.
Definition
Ether is a class of organic compounds that
contain an ether group — (an oxygen atom connected to R
two alkyl or aryl groups) — of general formula R–O–R’.
O
R'
Classification of Ethers
(I) Aliphatic Ethers
(II) Aromatic Ethers
Aliphatic ethers are those in which
R and R' are both alkyl groups.
Aromatic ethers are those in which
either one or both R and R' are aryl
groups.
Examples:
Example:
CH3CH2CH2CH2 O
Butylmethylether
CH3
CH3 O
O
Methyl phenylether
C6H5 O
Diphenylether
C6H5
Nomenclature:
A. Common Names.
In the Common system the ethers are named according to the alkyl
group bonded to the oxygen atoms.
The two-alkyl groups bonded to the functional group (- O -) are
written alphabetically followed by the word ether.
Examples
CH3 - O - C2H5
Ethyl methyl ether
O CH2CH3
Ethyl phenyl ether
O
O
Diethylether
Tert-butylmethyl ether
B. IUPAC System For Ethers
The names for ethers are based on the alkane name of the longest
chain attached to the oxygen.
 The shorter alkyl group and the oxygen are named as an alkoxy
group attached to the longer alkane.
methoxy
They are named as alkoxyalkanes.
propane
Numbering the longer alkane gives
CH3—O—CH2—CH2—CH3
alkoxy group
Alkyl Group
CH3CH3CH2(CH3)2CH(CH3)3CC6H5-
Name
Methyl
Ethyl
Isopropyl
tert-Butyl
Phenyl
1-methoxypropane.
Alkoxy Group
CH3OCH3CH2O(CH3)2CHO(CH3)3COC6H5O-
Name
Methoxy
Ethoxy
Isopropoxy
tert-Butoxy
Phenoxy
Examples
O
CH3
CH3
(a)
(b)
CH3CHCH2 O
3
2
CH3
1
1-Methoxy-2-methyl propane
Methoxy cylohexane
O
CH2CH3
H3C
(c) CH3CH2CH2
O CH2CH2CH2CH3
1
Propoxy butane
2
3
4
(d)
1-Ethoxy-1-methyl Cyclohexane
O
O
5-ethoxy-2-heptene
1-phenoxy-1-propene
O
O
Common:
Diphenylether
Methylphenylether
Anisol
IUPAC:
Phenoxy benzene
Methoxy benzene
Exercise:
1- Give the name of the following molecules (IUPAC & Common)
O
2- Draw the correct structure for the following
A) Methyl vinyl ether
B) Methoxy hexane
Physical Properties
1. Solubility of Ethers
• Ethers containing up to 3 carbon atoms are soluble in water, due
to their hydrogen bond formation with water molecules.
Ethers can form hydrogen bonds with water molecules
• The solubility decreases with increase in the number of carbon atoms.
• The relative increase in the hydrocarbon portion of the molecule
decreases the tendency of H-bond formation.
2. Boiling Points of Ethers
 Ethers have an O atom, but there is no H attached.
Thus, hydrogen bonds cannot form between ether molecules.
O
R’
R
Ether molecules cannot form hydrogen bonds with other ether molecules.
CH3CH2CH2CH3 CH3 O CH2CH3 CH3CH2CH2OH
Butane
Methoxyethane
1-Propanol
(butane)
(ethyl methyl ether)
(Propyl alcohol)
M.W. = 58
b.p. = - 0.5°C
M.W. = 60
b.p. = 7.9 °C
M.W. = 60
b.p. = 97.2°C
General methods of preparation of ethers
A- Dehydration of Alcohols.(only symmetric ethers)
• This method is used for industrially preparation for symmetric ethers.
• In the presence of acid, two molecules of an alcohol may lose water
to form an ether.
General Equation
R' OH + R" OH
H+
heat /140°C
R' O R" + H2O
Examples
2 CH3OH
2 CH3CH2OH
H2SO4
140°C
H2SO4
140°C
CH3 O
CH3
+
CH3CH2 O CH2CH3
H2O
+
H2O
B- Williamson Synthesis.
The reaction of a sodium alkoxide; RONa or a sodium phenoxide; ArONa
with an alkyl halide to form an ether is known as the Williamson synthesis.
- It is an important laboratory method for the preparation of symmetrical
and unsymmetrical ethers.
- The reaction involves nucleophilic substitution of an alkoxide ion for
a halide ion.
General Equations
R O- Na+
+
Sodium alkoxide
Ar O- Na+ +
R' X
Alkyl halide
R' X
Sodium phenoxide Alkyl halide
R O
R'
+
NaX
Alkyl ether
Ar O R' + NaX
Aryl ether
Examples
CH3CH2 O Na
CH3CH2Br
CH3CH2 O CH2CH3
O Na
O CH3
CH3I
!
NaBr
Na I
Note that
The alkoxide is commonly made by adding Na or K to the alcohol
Examples
+
O Na
OH
Na
OCH2CH3
CH3CH2
Br
+
sodium
cyclohexanol
OH
cyclohexyloxide
NaBr
ethoxycyclohexane
OCH3
1) Na
2) CH3-I
3,3-dimethyl-2-pentanol
2-ethoxy-3,3-dimethypentane
Reactions of Ethers
 Ethers undergo just one kind of basic chemical reaction:
cleavage by acids.
Cleavage of Ethers by Acides
 Ethers are cleaved by HX to an alcohol and a haloalkane.
General Equation
R O
R' + HX
Ether
Heat
R
X +
Alkyl halide
Conc. acid
R' OH
alcohol
Specific Example
CH3 O CH3 + HBr
Dimethyl ether
Heat
Hydrogen bromide
CH3 Br + HO CH3
Methyl bromide Methyl alcohol
Note: If two or more equivalents of acid are used further
dehydration can occur on formed alcohols which may react further
to form a second mole of alkyl halide.
Example
CH3CH2OCH2CH3
Diethyl ether
+
2 HBr
Heat
Excess
Hydrogen bromide
2 CH3CH2Br + H2O
Ethyl bromide
Cyclic Ethers; “Epoxides”
Epoxides
Definition
O
An epoxide
Epoxides or Cyclic ethers
 Epoxides are cyclic ethers in which the ether oxygen is part of a threemembered.
The simplest and the most important epoxide is ethylene oxide.
O
O
H C
H
H
H
H
H
Ethylene oxide
C H
H
General methods of preparation of Epoxides
Peroxide Epoxidation
Epoxides are often prepared from reacting with organic peroxy acids
(“peracids”) ex; CH3C(O)OOH in a process called epoxidation.
General equation
O
RCH CHR'
+
R"CO
OH
MCPBA
RCH
CHR'
O
Peroxy acid
Note that:
Epoxide
Cl
MCPBA=
CO3H
+
R''COOH
Example
CH3
CH CH2
phCO3H
H3C CH
CH2
O
propeneoxide
propene
MCPBA
CH2Cl2
O
Reaction of Epoxides
Ring-opening reactions of epoxides:
• Epoxides are highly strained and easily undergo ring-opening
reactions under both acidic and basic conditions.
• For the same reason epoxides have the tendecy to open up its ring.
Thus oxygen atom combines with the reactive hydrogen atom of
vairous compounds to form a hydroxy group, -OH, as shown in the
next slide.
General Equation
CH 2 + H Y
CH 2
O
Ethylene oxide
CH2 CH2
OH Y
Addition Product
Reaction of Epoxides.
H2O/H
CH3OH/H
CH2
CH2
OH
OH
CH2
CH2
OH
OCH3
1,2-Ethandiol
2-Methoxyethanol
O
CH2
CH2
+
HX/H
CH2
CH2
OH
X
RMgX/dryether
CH2
CH2
H3O
OH
R
Ethylene oxide
Ethylene halohydrin
2-Halo ethanol
Alkyl alcohol
Thank you
For your attention